1. Field of the Invention
The present invention relates to a vertical shaft impact crusher. More particularly, the present invention relates to a vertical shaft impact crusher for crushing bulk materials, for example, natural rock, into particles of predetermined diameter.
2. Description of the Prior Art
Bulk materials, e.g., natural rock, are crushed in accordance with various uses, for example, aggregate for concrete, paving stone, subgrade material, etc. One type of crusher used for such crushing process is known as vertical shaft impact crusher.
In the vertical shaft impact crusher, a rotor having a plurality of blades on the upper side thereof is rotated at high speed, whereby raw stone cast in the crusher is accelerated by the blades and centrifugally discharged so as to collide with anvils which are disposed in a ring shape around the rotor, thereby crushing the raw stone. During such crushing process, large impact force is applied to the blades and the anvils, so that these members are likely to become worn.
For this reason, manganese steel or other wear-resistant material is used for the blades and the anvils. However, even if such a material is used, wear of these members cannot be avoided, and these members must be frequently replaced with new ones. Various propositions have heretofore been made to reduce the frequency of replacement of these members.
As a proposition made for the purpose of reducing the frequency of replacement of anvils, for example, a vertical shaft impact crusher, which is disclosed in Japanese Patent Application Public Disclosure (KOKAI) No. 63-88054 (1988), is known. In this crusher, a stepped support block having a plurality of steps with different heights is provided on the inner wall of a crushing tank, and a hoop that supports anvils is supported on the stepped support block.
With the above-described crusher, the heightwise position of the anvils can be changed by shifting the position where the hoop is attached to the stepped support block. Accordingly, the range of collision between raw stone and the anvils enlarges in the heightwise direction, so that non-uniform wear of the anvils can be prevented to a certain extent. Therefore, the frequency of replacement of the anvils decreases.
However, the conventional vertical shaft impact crusher necessitates lifting the hoop from the outside when the heightwise position of the anvils is changed. In addition, the hoop must be rotated through a very small angle in order to position a vertical leg, which is provided on the lower side of the hoop, to the desired step of the stepped support block. Accordingly, the above-described crusher suffers from the disadvantage that the adjustment of the heightwise position of the anvils requires a troublesome operation and a great deal of time.
As a proposition made for the purpose of reducing the frequency of replacement of blades, for example, a vertical shaft impact crusher, which is disclosed in Japanese Patent Application Public Disclosure (KOKAI) No. 62-193657 (1987), is known. In this crusher, a pair of blades, which define a discharge passage, are provided on the upper side of a rotor in symmetry with respect to the radial direction, and the rotor is rotated forwardly and then backwardly, with a view to avoiding non-uniform wear of the blades. With this crusher, the range of collision between raw stone and the blades is enlarged by reversing the direction of rotation of the rotor, so that non-uniform wear can be prevented to a certain extent. Therefore, the frequency of replacement of the blades also decreases.
Raw stone is cast onto the rotor from above it, as described above. Accordingly, even in such an impact crusher, wear unavoidably concentrates on only the lower part of each blade. In addition, blades that are used in this type of crusher are heavy in weight. Therefore, maintenance is not easy.
Further, U.S. Pat. No. 4,090,673 discloses a vertical shaft impact crusher having an improved impeller table liner. However, the specification of this prior art does not explain improvement in wear of the blades and the anvils in detail.